Re: GSC 748-1618

[Chris Lloyd <cl@astro1.bnsc.rl.ac.uk>]

Michael,

I normally use the differential magnitudes when working with TASS data but
in this case they are certainly no better and probably worse. I enclose two
plots. The first shows the light curve of GSC748 relative to number 89632 in
the big list.

The filled symbols are the raw TASS magnitudes while the open symbols are
the differential magnitudes plus the mean of the comparison. In reality
there is very little to choose between them but to me the differential mags
have more scatter.

The second plot is the difference between two comparisons, 89632 and 89725
using the same phasing. The symbols are the same as before. Apart from the
few outliers I can see no obvious difference but the standard deviations are
0.023 and 0.029 for the raw and differential mags respectively. There is
clearly something afoot here because my experience is that the differential
magnitudes are usually significantly more reliable than the raw mags. I have
most of a technical note on this which I really must finish off. I suspect
that there is something up with the TASS data which generally increases the
noise but that doesn't explain why parts of the curve are systematically
different.

GSC 748-1618
 89720  135 103.5564   7.9413  2286.72869 11.406 0.130 0 10.645 0.074 0
 89632  194 103.4339   7.9736  2286.70740 10.477 0.017 0  9.050 0.027 0
 89725  143 103.5627   7.9019  2286.74822 10.878 0.023 0  9.665 0.014 0

Cheers,

Chris

gsc748_f1.png

gsc748_f2.png